#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<vector>
using namespace std;
class Solution {
    int ret, m, n;
    int step = 2;
    bool vis[20][20];
public:
    int uniquePathsIII(vector<vector<int>>& grid)
    {
        m = grid.size();
        n = grid[0].size();
        int begin = 0, end = 0;
        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (grid[i][j] == 0) ++step;
                if (grid[i][j] == 1)
                {
                    begin = i;
                    end = j;
                    vis[i][j] = true;
                }
            }
        }
        dfs(grid, begin, end, 1);
        return ret;
    }
    int dx[4] = { 0,0,-1,1 };
    int dy[4] = { -1,1,0,0 };
    void dfs(vector<vector<int>>& grid, int i, int j, int count)
    {
        if (grid[i][j] == 2)
        {
            if (count == step)  ret++;
            return;
        }
        for (int k = 0; k < 4; k++)
        {
            int x = i + dx[k], y = j + dy[k];
            if (x >= 0 && x < m && y >= 0 && y < n && !vis[x][y] && grid[x][y] != -1)
            {
                vis[i][j] = true;
                dfs(grid, x, y, count + 1);
                vis[i][j] = false;
            }
        }

    }
};